As is well known, moisture in a waveguide cavity causes attenuation of signals passing therethrough. Attempts to evacuate the waveguide cavity have failed in the past, since the seals eventually leak and moisture, as part of the entering air, has contaminated the interior cavity of the waveguide. A normal solution to the problem is to continuously pressurize the waveguide with dry air, so that air is always leaking out of the waveguide rather than being drawn in whenever the temperature changes are such that the pressure inside the waveguide is lower than the pressures outside.
The prior art approach of pressurizing the waveguide has involved an expense of several hundred dollars for a pump and occasionally a heater, plus the expenses of maintaining and operating this equipment.
In general, the prior art devices have situated the radio in a building using a fairly long waveguide to supply signals to the antenna.
As the signal frequencies get higher, it becomes more important that the distance between the radio and the antenna be kept short to minimize signal losses. In situations where the radio equipment is located near the antenna and is not protected from the environment by being inside a building, it also means that any pressurization equipment is also subject to environmental problems.
The present invention overcomes many of these problems in the prior art by attaching a desiccant vessel to a test port on the waveguide, and mounting the radio as close as possible to the antenna, so that the total waveguide length affected by moisture is minimized. In such a configuration, the pumping phenomena created by changes in temperature resulting in movement of air in and out of the waveguide, will pass all the air through the desiccant vessel rather than attempting to draw the air through joints in the waveguide. By attaching the desiccant vessel to the test port in an easily removable manner, this port can serve a dual function of normally providing dry air to the waveguide and, in special instances, serve as a signal level detection point for test equipment.
It is thus an object of the present invention to improve upon prior art approaches of minimizing moisture in a waveguide.